1. Field of the Invention
The present invention relates to a roll shaft for supporting a recording medium rolled up on the roll shaft, a recording medium supply apparatus for supplying the recording medium and a recording apparatus for recording characters on the recording medium.
2. Related Art
Rolled paper prepared by winding printing paper in the form of a roll is loaded onto a roll shaft before being mounted in the paper feeding unit of a printer. Then the rolled paper together with the roll shaft is rotated at the time printing is done and let out, whereby the rolled paper is fed off toward the recording head side. The feeding of the rolled paper, that is, the rotation of the roll shaft is made such that a paper feeding roller disposed on the downstream side of the paper feeding unit carries the rolled paper while pressure-holding the forward end of the rolled paper. Therefore, the roll shaft is unable to stop rotating because of inertia and continues to rotate for a while immediately after the paper feeding roller stops rotating, thus causing the feeding of the rolled paper to stop. The rolled paper is let out toward the paper feeding roller even after the paper feeding roller stops rotating and warped in between the paper feeding unit and the paper feeding roller.
The warp results in causing the rolled paper to produce an unfavorable curl, an undesirable crease and the like. When the feeding of the rolled paper is started by rotating the paper feeding roller again with the warp left, the warped portion is fed in first and then the rolled paper is fed in by starting the rotation of the roll shaft. However, a sudden change (surging) in the carrying resistance occurs and there is the possibility of causing an error in conveyance by the paper feeding roller. The unfavorable curl and the undesirable crease and the like and the error in the conveyance caused by the paper feeding roller badly affect printing quality.
Therefore, there has been proposed an arrangement to provide a torque limiter for controlling the rotation of a roll shaft. With this arrangement, the roll shaft is rotated so as to feed in rolled paper only in case where torque at a predetermined level or higher is applied by a paper feeding roller and the roll shaft is quickly stopped with the paper feeding roller stopped, so that the rolled paper is prevented from producing a warp. Moreover, the whole rolled paper is braked during the time the rolled paper is being fed in and because driving operation follows up the roll shaft of a braking source, the skew of the rolled paper can be suppressed.
When thin rolled paper is used, however, the rolled paper is only restrained longitudinally in the space between the roll shaft and the paper feeding roller and likely to produce creases because the rolled paper is free from any restraint in the lateral direction. Therefore, creases are prevented from being produced by sharply increasing the torque of the torque limiter to longitudinally pull the rolled paper as much as possible whereby to restrain such moving freedom in the lateral direction.
When the torque of the torque limiter exceeds the own weight of the rolled paper, the rolled paper is lifted up together with the roll shaft during the operation of manually rewinding the rolled paper after the rolled paper is set in the paper feeding unit and this brings about a so-called cog misalignment phenomenon in which the gears joined together on one side of the roll shaft are off its meshing, thus causing the roll shaft to rotate. Consequently, the rolled paper set straight becomes tilted and the problem in this case is that the rolled paper makes an oblique movement (skew).